西南某水电站地下厂房顶拱对穿监测锚索破坏分析

Analysis of the Failure of Perforative Monitoring Anchor Cable in Top Arch of the Underground Powerhouse in a Hydropower Station in Southwest China

西南某水电站地下厂房地应力较高。在开挖至高程575 m期间位于左厂0+77.1桩号的预应力对穿监测锚索出现破坏,部分相邻工作锚索锚具沉陷。经过对设计支护、施工工艺、监测数据进行系统综合分析认为:施工规范未对锚具与垫板的有效搭接面积进行明确要求,在围岩变形较大造成锚索荷载过大,容易因搭接面积过小,造成垫板局部剪切应力超过极限抗剪强度发生系统破坏。通过增大锚具和钢垫板搭接面积、监测锚索增设锚具进行测力计调平、在垫板上加工对中槽等措施能减少对穿锚索超载后的类似破坏问题。

In the underground powerhouse of a hydropower station in Southwest China,the in-situ geostress is relatively high.During the excavation of the powerhouse,failure of the left-side No.0+77.1 perforative monitoring anchor cable,and abnormal sinkage of the anchorages of several adjacent working anchor cables are observed.A comprehensive analysis of the supporting measures,construction techniques and monitoring data shows that the problem is caused by the local damage of the cushion plates.As the effective lap area between the anchorage and the cushion plate is not clearly specified in construction specifications,the actual lap areas of these anchor cables are sometimes not enough.Thus,once the deformation of the top arch surrounding rock is large,the loads of the cables are also large,which may lead to local shearing damages of the cushion plates.Correspondingly,some countermeasures are proposed,including the increasing of the effective lap area between the anchorage and the cushion plate,arrangement of additional anchorage in monitoring anchor cable,and machining of the centering groove on the cushion plates,which can effectively solve the problem.